Here is the full list of all 119 Torchlight II achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Defeat the Nether King in Elite difficulty
Defeat the Nether King as an Embermage
Purchase 100 items from the gambler
Have 10,000,000 gold
Have 50 friends
Die with a hardcore character
Have 1,000,000 gold
Break 10,000 breakables
Assemble TrillBot
Find a legendary item
Defeat Boletus Rex
Purchase 50 items from the gambler
Sell 5,000 items
Reach level 100
Obtain a tier 3 skill bonus
Use 10 maps
Find 10 secret rooms
Start a hardcore character
Defeat the Dark Alchemist
Defeat 500 champions
Destroy 10 socketed gems
Squish 1000 critters
Wear a completed armor set
Have 100,000 gold
Purchase 20 items from the gambler
Recover 10 gems from items
Begin new game plus
Use a map
Defeat Verona
Defeat Aleera
Defeat Marishka
Explode 10,000 enemies
Defeat Vyrax
Defeat the Nether King as a Berserker
Defeat the Nether King in Casual difficulty
Defeat the Nether King in Normal difficulty
Defeat the Nether King in Veteran difficulty
Defeat the Nether King
Defeat Killbot
Squish 500 critters
Defeat Thiss
Socket 50 gems into items
Defeat Cacklespit
Fish using dynamite
Defeat Bloatfang
Defeat the Grizzled Alpha
Deal 10,000 critical strikes
Defeat the Wraith Lord
Take 100,000 steps
Obtain a tier 2 skill bonus
Do 10,000 damage with a single attack
Add a friend
Have 10 friends
Break 1,000 breakables
Defeat the Siege Guardian
Defeat Ezrek Khan
Defeat the King In Masks
Use 500 potions
Defeat Aruk
Fish 100 times
Open 500 chests
Use an enchanter 50 times
Defeat 100 champions
Teach a pet 4 spells
Destroy a socketed gem
Take 50,000 steps
Squish 100 critters
Sell 500 items
Defeat Kidrik the Mauler
Deal 1,000 critical strikes
Defeat One-Eyed Willy
Recover a gem from an item
Join a multiplayer game
Defeat the Artificer
Defeat the Manticore's Mate
Defeat the Manticore
Explode 1,000 enemies
Open 100 chests
Learn 4 spells
Defeat Grand Regent Eldrayn
Defeat Chillhoof
Learn a spell
Use an enchanter 10 times
Defeat King Pogg
Defeat 25 champions
Obtain a tier 1 skill bonus
Take 10,000 steps
Defeat the Winter Widow
Use 50 potions
Socket a gem into an item
Defeat General Grell
Find a secret room
Break 100 breakables
Open 20 chests
Defeat Mordrox
Explode 100 enemies
Teach a pet a spell
Send your pet to town
Fish 10 times
Trade an item with another player
Defeat the Fallen Guardian
Start a multiplayer game
Defeat the Nether King with each of the 4 classes
Defeat the Nether King as an Engineer
Defeat the Nether King in hardcore mode (casual)
Defeat the Nether King in hardcore mode (elite)
Defeat the Nether King in hardcore mode (normal)
Defeat the Nether King in hardcore mode (veteran)
Defeat the Nether King as an Outlander
Deal 100,000 critical strikes
Use an enchanter 500 times
Fish 1,000 times
Recover 100 gems from items
Destroy 100 socketed gems
Find 100 secret rooms
Sell 50,000 items
Socket 500 gems into items
Use 100 maps
Use 5,000 potions